The present invention relates to a fuel tank for motor vehicles which is connected to a supplementary tank containing a flame-coloring additive, where a data recorder causes, in the event of a fault signal, the flame-coloring additive to be added to the fuel tank from the supplementary tank, and to a process for adding a flame-coloring additive to the fuel in the fuel tank.
Fuel cell driven motor vehicles either contain a storage tank for hydrogen or firstly generate hydrogen from alcohols by means of a reforming catalyst and then use this hydrogen in a second step in the actual fuel cell to generate electric current for driving the vehicle (see, for example, xe2x80x9cHightech Report ""98xe2x80x9d, Daimler Benz AG, Public Relations, 70546 Stuttgart). The latter vehicles, like those driven by conventional internal-combustion engines, require fuel tanks to hold the liquid fuel. However, the alcohols used as fuel, especially methanol and ethanol, burn with a pale bluish or virtually invisible flame, in contrast to gasoline or diesel fuels. This property of alcohols represents a considerable safety risk for the operation of motor vehicles having fuel cells. If the tank is damaged in an accident and the alcohol escapes and ignites, the alcohol flame can remain undetected. People in the vicinity are therefore exposed to considerable risk due to combustion or explosions. In addition, extinguishing work is made more difficult.
It is therefore necessary to add flame-coloring additives to fuels for fuel cell driven motor vehicles in order to ensure that flames are seen easily and rapidly. Flame-coloring additives are known in principle. For example, alcohol flames can be colored, for example, using alcohol-soluble compounds of the alkali and alkaline earth metals and in particular using boron compounds. Addition of just 0.2% by weight of ethyl borate ensures an intensely green flame. It is also possible to use unsaturated organic compounds, such as aromatics, which tend to form soot and burn with a luminous flame.
However, a disadvantage of such additives is that, even at low concentrations, they completely or partially poison or reduce the life of the reforming catalyst which precedes the fuel cell. In addition, some of the additives (for example aromatics) have a toxicity problem, which means that broad use thereof is not readily possible.